Former Giants slugger Barry Bonds tested positive for steroids in November 2000, the year before he set baseball's single-season home run record, federal prosecutors said Thursday.

In documents filed in U.S. District Court in San Francisco, the government provided new details on its claim that baseball's home run king had failed multiple tests for banned drugs and then lied about it to the grand jury investigating the BALCO steroids scandal.

In November, when Bonds was indicted on five counts of perjury and obstruction of justice, the government first claimed that investigators had seized "positive tests" for Bonds in their probe of BALCO but gave no specifics.

The explanation is contained in the documents filed Thursday in connection with Bonds' upcoming trial on perjury charges.

Bonds has pleaded not guilty, and in his 2003 grand jury testimony repeatedly denied ever using banned drugs.

Major League Baseball didn't begin steroid testing until 2003. A source familiar with the case previously disclosed that Victor Conte, founder of the Bay Area Laboratory Co-Operative in Burlingame, had arranged for private steroid tests for Bonds to test the results of his BALCO drug regimen.

Federal agents seized a trove of documents regarding banned drug use in 2003 raids on BALCO and on the Burlingame home of Greg Anderson, Bonds' trainer, court records show.

In the filing, the government said that at trial it would produce evidence showing that Anderson provided Bonds with steroids before a positive test dated November 2000.

The test report, marked "Barry B," showed positive results for two anabolic steroids, the government said.

In 2000, Bonds, then age 35, batted .306 with 49 home runs. The following year he hit 73 home runs, surpassing the single-season mark of 70 set by St. Louis Cardinal slugger Mark McGwire in 1998. Both sluggers have been the focus of steroid allegations.

The government made the disclosures in a motion asking Judge Susan Illston to allow the five-count indictment to go to trial as handed up. Last month, Bonds' legal team had asked the judge to dismiss parts of the indictment and pare back others, arguing that prosecutors had asked Bonds "fundamentally ambiguous" questions when he testified before the grand jury.

But the government said Bonds clearly understood the import of the prosecutor's questions.

"Bonds denied that he ever knowingly took steroids provided by Anderson," the government wrote in the filing. At trial, prosecutors said, the government's evidence will show that Bonds received steroids from Anderson in the period before the November 2000 positive drug test.